This invention relates to valves and more particularly to a hybrid butterfly valve having a rotatable and slidable closure disk providing the full flow advantages of a butterfly valve and the throttling and sealing advantages of globe and needle valves.
The high flow rate and relatively low pressure drop at full flow are some of the advantages that butterfly valves have over other valves. Other advantages include simplicity of operation, compact valve body and relatively low cost. However, balanced against these advantages butterfly valves have high valve seat wear and inability to maintain a tight seal. Additionally, if the valve is used to throttle the fluid flow or to frequently cycle to open and closed positions, these disadvantages are amplified and additionally frequent repair is required. Globe and needle valves, on the other hand, have good sealing and throttling capability because the valve disk or plug position can be closely regulated. Furthermore, because of the linear movement of the valve disk and its ability to be closely positioned within the valve seat, good sealing can be obtained.
The following art was reported as being the most pertinent located in a search conducted prior to the filing of the present application, and except for Bliss U.S. Pat. No. 1,669,119, and Topham et al., U.S. Pat. No. 3,780,983; this art is substantially deficient in regard to the present invention and is cited merely in fulfilment of applicant's duty of disclosure: U.S. Pat. Nos. 1,669,119 (Bliss); 1,722,752 (Karnath); 3,300,177 (Topham et al); 3,583,699 (Campbell); 4,206,903 (Scaramucci); and 4,693,451 (Tricini). Additionally, Italian Patent No. 503263 issued Dec. 4, 1954 was cited.
In Bliss, U.S. Pat. No. 1,669,119, and Topham et al., U.S. Pat. No. 3,780,983, a valve includes a cam for pressing the valve disk into the valve seat, and in Topham et al for unseating the valve seat, but these systems require springs to hold the disk to the rotating shaft during rotary motion of the disk. These springs also oppose the torque of the valve actuator when seating of the disk occurs both directly and through increased friction forces between the cam and the disk. Additional deficiences of such springs are readily apparent, especially in cryogenic environments where thermally induced stresses, variations of metallic elasticity properties due to thermal excursions, and thermally accelerated fatigue occurs, and in which substantially no leakage is tolerable. An additional concern of the prior art is the method and structure for guiding the disk motion to ensure that rotary and linear motion of the disk occur at separate times and in the correct sequence. Any significant frictional forces occuring between sliding members may result in unbalanced or improper seating of the disk into the valve seat when combined with thermal expansions and contractions in cryogenic applications.